Data communications over radio frequencies dates back well over 100 years to a time when Morse code was used for telegraphy and ship to shore communications systems. Some of the earliest “spark gap” transmitters sent a series of dots and dashes over long distances using a broad range of radio frequencies. As vacuum tube technology advanced, so-called “continuous wave” (CW) transmitters were developed that allowed an operator to switch a radio carrier on and off to thereby transmit sequences of letters, numbers and special characters. Such messages were sometimes encrypted.
Many current messaging capabilities over existing LSW/HFR frequencies and associated systems are rooted in these old signaling methods. For example, High Frequency (HF) radio frequencies are between 3 and 30 MHz, also known as the decameter band or decameter wave, as the wavelengths range from one to ten decameters (ten to one hundred meters). The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Such radio frequencies have been used for many decades for Morse code as well as radiotelephone (voice) and more recently for data packet radio. Because radio waves in this band can be reflected back to earth by the ionosphere layer in the atmosphere, called “skip” or skywave propagation, these frequencies can be used for long distance communication, at intercontinental distances (1000 Kilometers).
However, as communications technology has evolved, and with the advent of cellular, satellite, or other digital transmission mediums, the use of LSW/HFR for communications has been significantly deemphasized. This can be easily seen with the advent of the Internet, as most individuals or organizations today use either cellular, Wi-Fi, satellite, or other terrestrial based communications mediums for exchanging information with their peers. For example, in the 1980's Phillip Karn developed the KA9Q package to transmit TCP/IP (Internet) base communications over amateur (ham) packet radio on HF frequencies such as used on the 160-meter through 2-meter ham bands (e.g., 1.8. MHz to 148 MHz). Much of this functionality is still available today and has been subsumed into the current day Linux operating system. When this technology was originally developed, security about the exchange of information was not necessarily paramount. Furthermore, given LSW/HFR's relatively low transmission speed as compared to the multimegabit bandwidth achievable today, this technology has fallen out of favor.
It would be desirable to enable secure messaging over LSW/HFR technology. Consider an event such as natural catastrophe (earthquake, hurricane, tornado, tsunami, etc.). Many of today's technologies rely on large infrastructure components such as cellular base stations or network interconnects to enable the flow of data between each of the end nodes. In the case of a natural disaster, these infrastructure components can be easily compromised, or taken out of service because access to power or data interconnect services have been interrupted.
Therefore, there is a need to provide a solution that enables the exchange of secure messages between peers that interfaces with common off the shelf components (COTS), and does not need to depend upon regional or local infrastructure. Alternatively, this same solution may enable an “off grid” path for the exchange of secure messages where privacy over third party controlled infrastructure is not achievable.